Rear Diff Additive

**theorangeguy** · 06-24-2014, 07:06 AM

Had my rear end fluid changed about 3-4months ago and I have noticed that it is whining more than usual "specifically at interstate speeds"...I know the GM Additive was not used and they put synthetic oil in the rear end. Do you guys recommend the GM Additive? I've read quite a few threads on this subject and seen some people say yes and some people say no.

**2002ssslp** · 06-24-2014, 05:16 PM

Yes. Get the GM additive and change you gear lube to conventional "Dino" oil. Our rears are weak enough, don't help it to an early grave.

**theorangeguy** · 06-24-2014, 05:52 PM

Originally Posted by 2002ssslp

Yes. Get the GM additive and change you gear lube to conventional "Dino" oil. Our rears are weak enough, don't help it to an early grave.

so switch to non-synthetic and add the additive?

**98TransAmWs-6** · 06-24-2014, 06:43 PM

I just used synthetic with the additive in it already and I haven't had any issues and it has been like that for a couple of years.

**pajeff02** · 06-25-2014, 02:26 AM

Even though the stock rear has a torsen type posi that utilizes gears rather than clutches GM recommends the use of the additive to combat what is described as a "rusty screw" type noise. I have also read that dino oil is recommended over synthetic, but I have never seen a good explanation for this.

**0rion** · 06-25-2014, 02:29 AM

you'll most likely get answers all over the place for this as everyone seems to have their own way of doing it. This is another example of where I try not to over think things and stick with factory recommendations. My strange rear specifically said not to use synthetic and to run additive. The lack of additive really shouldn't make your rear whine though....it would make it chatter. The synthetic could possibly be why your rear seems a little louder. Personally unless it's really loud I wouldn't worry about it too much but then again.....I wouldn't run synthetic in there and would have the additive.

**2002ssslp** · 06-25-2014, 05:10 AM

Originally Posted by theorangeguy

so switch to non-synthetic and add the additive?

YES

**cammed goat** · 06-27-2014, 04:19 PM

The additive allows the differential disconnect going through turns without making any noise. The additive doesn't reduce noise. Only the gear oil reduces the noise and lubricates the carrier bearings.

**0rion** · 06-27-2014, 11:26 PM

the friction modifier can make noise ( or lack of it rather) but the noise will be a chatter through turns. It's due to the clutches not engaging and disengaging smoothly across the face of the clutch. The question really becomes does the modifier effect the weight of the gear oil? I'm sure it does but how much I don't know. A thicker oil will be quieter but rob more HP. I go back to my original statement though......if you're unsure stick with what the factory recommendations are.

ps
I'm pretty drunk right now